The present invention is a process for removing epoxy compositions from a substrate and especially for removing cured epoxy compositions employed as the backseal without removing silicone materials employed as the topseal for integrated circuit chip modules.
During the preparation of integrated circuit modules, input/output (I/O) pins are inserted into the substrate of the module. Attached to the backside of the substrate is at least one integrated circuit chip. The input/output pins provide the needed electrical connections to the integrated circuit chips on the backside of the substrate or carrier. A topseal of a silicone gel, such as Sylgard (trademark of Dow Corning Corporation), is used to protect the chips from alpha-particle emissions from the substrate material. After application of the Sylgard, the assembled module is placed in a vacuum to flow the Sylgard into the space between the chip and the substrate. Sylgard also remains on top of the chip, although this is not needed for protection from alpha particles. The chip carrier or substrate is placed inside a cap or container with the backside of the carrier being covered by the bottom of the cap or container. The backside of the carrier or substrate on which is attached at least one integrated circuit chip is hermetically sealed to the cap or container, such as by employing certain epoxy compositions. The compositions are employed in order to protect and seal the electrically active portions of the module.
In many situations it is desirable to be able to remove the cap in order to make engineering changes or to replace or repair the semiconductor devices on the carrier. This removal of the cap must be done without destroying the rest of the module so that it can be worked on and reused. It is often desirable to remove the cap without also removing the topseal material from behind the chip (between the chip and the substrate), thus eliminating the need to replace the topseal after rework.
The difficulty has been to provide a composition capable of removing the cured epoxy backseal without removing the silicone topseal from behind the chip and without adversely affecting the rest of the module. Since such a composition will be used in a manufacturing environment, it must be safe and non-toxic. Clark et al., "Nondestructive Chemical Removal of Encapsulants Used in Semiconductor Packaging," IBM Technical Disclosure Bulletin, vol. 23, no. 12, May 1981, p. 5285, discloses a solvent having about 95% by volume n-butylamine and about 5% by volume of oleic acid for removing organic epoxies, such as Scotchcast (trademark of 3M Company) 5239, from semiconductor chip packages. However, the mixture also removes silicone gels, such as Sylgard, from behind the chips. Moreover, it has been determined that this mixture cause low levels of corrosion of Al-Cu metallurgy. Finally, the mixture has a flash point of -1.degree. C., which is unacceptably low from a safety standpoint.
A mixture of pyridine and dimethyl sulfoxide (1:0 to 1:2) has been used to remove hardened photoresists. (Linde, et al. "Novel Solvent Soak for the Removal of Hardened Photoresists," IBM Technical Disclosure Bulletin, vol. 26, no. 12, May 1984, p. 6303.) However, there is no suggestion that mixtures of pyridine or substituted pyridines with sulfoxides are capable of removing cured epoxy and no suggestion that they will remove cured epoxy without attacking Sylgard.